1. Field of the Invention
The present invention relates to an electrode for a fuel cell, and a membrane-electrode assembly and a fuel cell system including the same. More particularly, the present invention relates to an electrode for a fuel cell having a high catalyst activity, and a membrane-electrode assembly and a fuel cell system including the same.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and a fuel (e.g., hydrogen or a hydrocarbon-based material, such as methanol, ethanol, natural gas, etc.).
A fuel cell includes a stack composed of unit cells and produces various ranges of power output.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell that uses methanol as a fuel.
The polymer electrolyte fuel cell has a high energy density, but requires a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce a hydrogen-rich gas as the fuel gas.
By contrast, a direct oxidation fuel cell has a lower energy density than that of the polymer electrolyte fuel cell, but it does not need an additional fuel reforming processor. Therefore, it can be used as a portable power source for small and common electrical equipment.
In the above-mentioned fuel cell system, the stack that generates electricity substantially includes several unit cells stacked adjacent to one another, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly is composed of an anode (also referred to as a “fuel electrode” or an “oxidation electrode”) and a cathode (also referred to as an “air electrode” or a “reduction electrode”) that are separated by a polymer electrolyte membrane.
A fuel is supplied to the anode and adsorbed on one or more catalysts, and the fuel is oxidized to produce protons and electrons. The electrons are transferred into the cathode via an out-circuit mechanism, and the protons are transferred into the cathode through the polymer electrolyte membrane. An oxidant is supplied to the cathode, and the oxidant, protons, and electrons are reacted on a catalyst at the cathode to produce electricity, along with water.